1. Field of the Invention
The present invention relates to the preparation of a dough adopted for incorporation into compositions which are vulcanizable into elastomeric state by a polyaddition reaction, namely, by a crosslinking reaction between a polydiorganosiloxane containing at least two .tbd.Si-CH=CH.sub.2 groups (abbreviated SiVi groups) in its molecule and a polysiloxane containing at least two .tbd.SiH groups in its molecule. Once vulcanized (crosslinked), these compositions form silicone elastomers and such compositions are vulcanizable at room temperature or at higher temperatures (generally lower than 200.degree. C.).
2. Description of the Prior Art
Compositions of the above general type are known to this art, and are typically two-pack (two-component) compositions, i.e., they are marketed in two packages, the contents of which must be mixed at the time of use. The preferred catalyst employed for crosslinking these compositions is in most cases a complex compound of platinum such as, for example, that prepared from chloroplatinic acid and 1,3-divinyl-1,1,3,3-tetra-methyldisiloxane, according to U.S. Pat. No. 3,814,730. Other platinum complexes are described in U.S. Pat. Nos. 3,159,601, 3,159,662 and 3,220,972.
In such two-pack compositions, one of the packs contains, for example, a dough (based on polysiloxane containing SiVi functional groups and silica) to which at least one polysiloxane containing an SiH functional group has been added with stirring; part A is thus provided. The other pack (part B) contains the catalyst for the polyaddition reaction, for example in addition to the dough described above.
Such compositions can also be presented in a single pack (in which case they are designated single-component compositions) and they then contain, in known manner in the same pack, the components of the above parts A+B and an inhibitor of platinum, such as those described, for example, in U.S. Pat. Nos. 3,445,420 (acetylenic alcohols) and 4,061,609 (hydroperoxides), which ensures that the compositions do not vulcanize until they are removed from the package (in air) or after they have been slightly heated.
In the prior art techniques for formulating the compositions described above, a dough is generally first prepared, in a trough kneader, from the polysiloxane containing an SiVi group, silica, water and hexamethyldisilazane, and the mixture must be kneaded for a number of hours (at least three hours).